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2–14
on values of 0, 1, 2, or 3 which correspond to division factors of 1, 2, 4, or 8. The Q-divider register (Q) is
stored in bits 2 – 0 of the MCLK/loop clock control register (index: 0x39) and can take on values of 0, 1, 2,
. . ., 7 which correspond to division factors of 2, 4, 6, . . ., 16. The total post-scalar frequency division factor
is:
F
VCO
4
F
D
Z
2
P
1
(Q
1)
(65
N)
K
(7)
Next, set F
VCO
to the lower limit of 110 MHz and solve for Z:
27.5
(65
F
D
Z
N)
K
(8)
Finally, determine the P and Q values:
IF Z
16 then P
TRUNC (log
2
Z), Q
0
IF Z
16 then P
3, Q
INT
Z
16
16
1
Set bits 7,6 of the N-value register to 1,1 (default). Set LES1 and LES0 in the M-value register (bits 7,6) to
0,0 (default). Set bits 7–2 of the P-value register to 1111 00. This enables the PLL to oscillate and disables
the LCLK edge synchronizer function, which is only used for packed-24 modes. To reset the PLL by resetting
bit 7 of the P-value register to 0.
2.4.3.2
For packed-24 modes, the loop clock PLL is programmed according to Table 2–15. The LCLK edge
synchronizer delay (M-value register bits 7 and 6) depends on whether the graphics accelerator is driving
the VRAM shift clock (true color control register bit TCR5 is cleared to 0) or the TVP3026 is driving the VRAM
shift clock (TCR5 = 1). See subsection 2.6.6, Packed-24 Mode for a typical setup procedure for packed-24
modes. As shown in Table 2–15, a different setting is required for the M-value register in the 4:3 multiplex
mode depending on the silicon revision. Software can determine the silicon revision by reading the silicon
revision register at index 0x01 (a value
≤
0x20 indicates revision A and
≥
0x21 indicates revision B).
Programming for Packed-24 Modes
Table 2–15. Loop Clock PLL Settings for Packed-24 Mode
PACKED-24 MODE
BIT TCR5
(Index 0x18)
N-VALUE REGISTER
M-VALUE REGISTER
TVP3026A
M-VALUE REGISTER
TVP3026B
4:3
0
0xFD
0
×
F9
0
×
FC
0
×
FC
0
×
FD
0
×
F9
0
×
FC
0
×
FC
0
×
BE
0
×
BE
0
×
3D
0
×
7F
0
×
3E
0
×
3E
0
×
BD
0
×
FF
0x3E
0
×
BE
0
×
3D
0
×
7F
0
×
BE
0
×
3E
0
×
BD
0
×
FF
8:3
0
5:4
0
5:2
0
4:3
1
8:3
1
5:4
1
5:2
1